Printer calibration has become an important topic as print resolution and color reproduction improve in printers. Color calibration compensates for color inconsistency due to manufacturing variations in ink drop weight, ink chemistry and the environmental effects of temperature and humidity on the printing process. For example, ink drop weight produced by different print heads often varies as a result of minute manufacturing differences in the size of the nozzles used in an inkjet print head, different resistor characteristics in the heater element used to eject the ink droplets in the inkjet print head, variations in the orifice shape, or any other difference from one print head to another. Differences in the ink chemistry combined with temperature and humidity also affects the final color appearance when applied to a print medium. To accommodate these factors, color calibration modifies the number of ink drops during printing to make color printing more consistent.
Techniques for color calibration may be time consuming. In some techniques, a non-trivial number of printer test patches are printed in the primary ink or color being calibrated in the print head. For a four color pen, producing a test ramp can include at least 17 patches for each pen having an increment in gray level of 16 units between each of the gradients or a total of 68 patches.
If the printer mechanism is able to conduct the print medium forward and then in reverse, the different patches are printed and then reversed for measurement by the embedded sensor on the printer. However, if the printer does not have a paper reverse feature, each portion of the test patch may be printed swath by swath and then allowed to dry prior to taking sensor measurements. This can take a non-negligible time as a four-color pen involves printing 17 patches for 4 different colors, or a total of 68 patches. For print heads using a greater number of pens, an even longer time period may be involved as significantly more patches must be printed. For example, a six-color pen (i.e., CcMmYK) involves printing 17 patches for each of the 6 colors for a total of 102 patches.
Even when the patches are printed, an additional time delay is incurred as they are scanned and processed. An embedded sensor built into the printer and mounted by the print head takes time to scan the patches and detect the optical density of the ink printed. Of course, some people will not run these calibration routines as the time delay for printing, sensing, and processing the numerous patches is significant. Accordingly, these printers will not be properly calibrated and will produce inconsistent colors and less-than optimal print results.